Space station glitch puzzles the experts

What should happen, but didn't
The computers normally operate in three pairs, where one computer (called the central unit) specializes in overall commanding and the other (the terminal unit) handles guidance, navigation, and control functions. The three pairs provide redundancy, via a special control software developed by the German aerospace firm DARA, which is now part of the European Astrium consortium.

When random errors upset any member of the pairs, it is "voted out" and the remaining pairs continue in control. When the last pair fails, an automatic restart sequence is triggered and all three pairs are brought back on line. This happens with some regularity, Suffredini stated, but the restart has always been successful until now.

“Something has changed in the environment” in the last few days, Suffredini said. It didn’t work on Wednesday, and apparently it still refused to work Thursday morning.

“We are in meetings discussing techniques and options to resolve what is causing this,” Suffredini said Wednesday night.

The cause could be external space radiation, or different ion charging on the station’s differently shaped exterior as it speeds through the upper ionosphere. It could be electromagnetic interference from new equipment, or old equipment operating in new ways, or interference from powerful radar or radio transmissions from Earth or from passing satellites. It might even be software, although no new programs had been installed recently.

Just this week, astronauts installed a new truss structure on the space station and unfurled two 115-foot-long (35-meter-long) sets of solar panels — and that addition has sparked the most speculation in the debate over the cause of the glitches.

“We did add another power source,” Suffredini noted. “Is there anything about that power source, the power quality coming from that [new] element, that might be causing this?” he wondered.

The Russians will be testing their computers using only power from their own solar panels, and NASA plans to help by disconnecting the new solar power wing briefly during another restart attempt.

Identifying the source of such interference, however, is not a solution unless the interference can be eliminated at least episodically to allow the computers to reboot and run for at least several hours a day.

Fixing the problem on a permanent basis might require significant hardware modifications and a great deal of time. Like NASA's next shuttle visit, Russia's next robotic supply shipment is due for launch in August — and the Russian cargo ship can’t dock unless the station’s computers are already functioning.

Terminal consequences
Suffredini held off from predicting what steps NASA would take if the computers could not be revived before the departure of the shuttle. “We’ll have to talk about that,” he said.

Although the U.S. gyroscope system recently validated a new rotational control technique that eliminated the need to use Russian thrusters for gentle turns, there are other occasions when those thrusters are still critical — such as maneuvers to avoid orbital debris.

The thrusters are also needed when the shuttle undocks from the station. The force shift places a sudden, strong torque on the station’s structure. In such situations in the past, the gyroscopes quickly were overwhelmed and called on rocket thrusters for assistance in holding the desired orientation.

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Without thrusters, the station would begin turning aimlessly until perhaps the gentle torque of the gyroscopes gradually brought it into a new equilibrium. But until then, electrical power generation would seriously suffer as the solar arrays pointed in less-than-optimal directions relative to the sun.

The worst-case scenario would call for evacuating the station, and that might lead to permanent abandonment if the attitude control system was inoperative and some unheated sections froze up. Suffredini said that having a crew on board always provided the most flexibility in controlling the station under "off-nominal" situations. The crew would always have the option of departing in the docked Soyuz spacecraft, if no hope remained for the station. But even that option requires the station not to be tumbling too quickly.

Suffredini said he saw no need to think that far ahead, not with a slew of diagnostic and recovery techniques even now being developed. He said he didn't expect to be telling journalists "we haven’t solved the situation" a few days from now. Odds are that Suffredini and his team, along with their Russian and European colleagues, will solve the situation — and it will go down as one of the greatest saves in the space station's nine-year history.

James Oberg, space analyst for NBC News, spent 22 years at NASA's Johnson Space Center as a Mission Control operator and an orbital designer.

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